If you look at "performance on the field" and not a lot of gibberish from draft geeks and Combine Crazies, Marshall has shown that he is better than average as an outside linebacker. He cannotplay middle linebacker in a 4-3 defense without at least one monster in front of him to keep blockers off him - which is what he had to try to do last season - but he has shown that he's more than adequate as an OLB.
So far, Rocky has shown
on the field that he can forget when he's supposed to be in the lineup and that he can bite on play-fakes really badly. Oh, he can also run around like a madman and jump on a tackling pile as the fifth man in.
Based on
demonstrated performance, Marshall is so superior as an OLB, it isn't even worth discussing. But just like the backup QB in most towns is the most popular guy around, Rocky seems to enjoy the same reputation here.
He MIGHT be really good; it is also possible that you've seen already the best he has to offer. And what you've seen so far ON THE FIELD is that he's way below adequate as a full-time linebacker at the NFL level.